Conventionally, as described in Document 1 (JP 2010-287372 A), an LED illumination system that includes a dimmer, a power supply device, and a light source device has been proposed.
The power supply device of the LED illumination system described in Document 1 includes an AC/DC converter and a dimming interface. The dimming interface is configured to superpose a dimming signal from a dimmer on a DC voltage obtained from the AC/DC converter. The light source device includes a current controller and an LED light source device. The current controller is configured to receive a voltage (a signal superposed voltage) from the dimming interface and to light the LED light source device by a power supply, which the signal superposed voltage is employed as, while controlling the light output of the LED light source device based on the signal superposed voltage.
Notably, the dimming interface of the LED illumination system described in Document 1 has a complex circuit configuration, and includes at least seven transistors. It is possible that a loss (such as switching loss) in the seven transistors will be large. That is, it is difficult to reduce the loss in the aforementioned dimming interface.